Thanks for the link. I've used this script before and it's very handy. However, notice that my page numbering needs to be in sets of 3, so applying master pages to every 3rd page solves only part of the equation. So, any ideas on how to do that?

I've used the script in that way also, and it works great. But again, my challenge is creating sets of pages that follow a series, such as 3 page 1's, 3 page 2's, 3 page 3's and so on... hope this makes sense.

I'm probably missing something here, but each page in the document has both an index and a name. You can control the name in the Numbering and Section Options panel, so that you can have three pages named "1" at the beginning of the document. But the index is the position of the page within the document, starting with 0. So app.activeDocument.pages[1] is the second page in the document no matter what it's been named.

Sounds to me like you need to apply one master to pages 0 through 2, and a different master to pages 3 through 5, etc.